File.open with block (auto-close) in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code using File.open with a block?

Consider the following Ruby code snippet:

File.open("test.txt", "w") do |file|
  file.puts "Hello, world!"
end
puts File.exist?("test.txt")

What will be printed when this code runs?

Ruby

File.open("test.txt", "w") do |file|
  file.puts "Hello, world!"
end
puts File.exist?("test.txt")

A nil

B true

C false

D An error is raised

💡 Hint

Think about whether the file is created and closed properly after the block.

The File.open method with a block automatically closes the file after the block finishes. The file "test.txt" is created and written to, so File.exist?("test.txt") returns true.

❓ Predict Output

intermediate

What does this code print when reading a file with File.open and a block?

Given a file "data.txt" containing the text "Ruby Rocks!", what will this code output?

File.open("data.txt", "r") do |file|
  puts file.read
end

Ruby

File.open("data.txt", "r") do |file|
  puts file.read
end

A An error is raised

B An empty line

C Ruby Rocks!

D nil

💡 Hint

Remember that file.read reads the entire content of the file.

The block reads the entire content of "data.txt" and prints it. Since the file contains "Ruby Rocks!", that is printed.

❓ Predict Output

advanced

What error does this code raise when using File.open without a block but forgetting to close?

What happens when you run this Ruby code?

file = File.open("example.txt", "w")
file.puts "Hello"
# No file.close called

Ruby

file = File.open("example.txt", "w")
file.puts "Hello"

A IOError: not closed

B RuntimeError: closed stream

C SyntaxError

D No error, but file remains open until program ends

💡 Hint

Think about what happens if you don't explicitly close a file in Ruby.

If you open a file without a block and don't close it, Ruby does not raise an error immediately. The file stays open until the program ends or the object is garbage collected. This can cause resource leaks but no immediate error.

🧠 Conceptual

advanced

Why is using File.open with a block preferred over without a block?

Which of the following is the main advantage of using File.open with a block?

A It automatically closes the file after the block finishes

B It speeds up file reading

C It prevents any errors from occurring

D It makes the file read-only

💡 Hint

Think about resource management and safety.

Using File.open with a block ensures the file is closed automatically after the block ends, preventing resource leaks and errors from forgetting to close the file.

❓ Predict Output

expert

What is the output of this Ruby code using File.open with a block and exception handling?

Consider this Ruby code:

begin
  File.open("missing.txt", "r") do |file|
    puts file.read
  end
rescue Errno::ENOENT
  puts "File not found"
end

What will be printed when this code runs and the file "missing.txt" does not exist?

Ruby

begin
  File.open("missing.txt", "r") do |file|
    puts file.read
  end
rescue Errno::ENOENT
  puts "File not found"
end

A File not found

B nil

C An unhandled exception is raised

D An empty line

💡 Hint

Think about how exceptions are handled in Ruby.

The code tries to open a file that does not exist. This raises Errno::ENOENT, which is rescued and prints "File not found".